I`ve done loads of these but only have this problem when there are small fragments of glass there that I have missed. your right not to stick it down yet as it should lay nice and flat with no issues, is it all corners that are like this? When I do them I remove everything from the phone and heat it upto 280deg then push and scrape under the glass to get it off, I can get the job done in under 45mins quite easily. I suggest you maybe strip the battery, logic board and speaker out to remove any pressure that maybe warping the underside and see if that helps, and if it does then glue the back on and clamp it up until its set solid then rebuild it.
Usually the wavy lines on white background are from too much heat when separating glass, try 65-70deg. Try the 8333 but don't just squirt loads on, apply it onto a dust free cloth placed on the LCD so to minimise it getting behind the backlight.
An epoxy would be good, we use b700 but tbh its no very good, ive used superglue it is great but you literally have one chance to get it right. I`ve heard t700 is ok too. I would look at epoxy as it will give enough time to adjust and give a good bond.